CentOS SSH Installation And Configuration

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How do I install and configure ssh server and client under CentOS Linux operating systems? Can you explains CentOS SSH installation commands?

OpenSSH is a free and open source software for remote login and running commands on CentOS enterprise Linux server or desktop systems. In this tutorial, we will learn how to install ssh server/client and configure the same.


CentOS SSH Installation

You need to install the following packages (which are installed by default until and unless you removed it or skipped it while installing CentOS):

  • openssh-clients : The OpenSSH client applications
  • openssh-server : The OpenSSH server daemon

Let us see all steps in details.

OpenSSH Installations under CentOS Linux

To install the server and client type the following command as root user:
# yum -y install openssh-server openssh-clients
CentOS SSH Installation

CentOS 6.x and older commands

Start the service:
# chkconfig sshd on
# service sshd start

Make sure port 22 is opened:
# netstat -tulpn | grep :22

Firewall Settings For CentOS 6.x and older

Edit /etc/sysconfig/iptables (IPv4 firewall),
# vi /etc/sysconfig/iptables
Add the lines:

Replace RH-Firewall-1-INPUT with actual chains in your config file. See CentOS/Redhat (RHEL 6.x) tutorial page for more info.

-A RH-Firewall-1-INPUT -m state --state NEW -m tcp -p tcp --dport 22 -j ACCEPT
If you want to restict access to, edit it as follows:
-A RH-Firewall-1-INPUT -s -m state --state NEW -p tcp --dport 22 -j ACCEPT
If your site uses IPv6, and you are editing ip6tables, use the line:
-A RH-Firewall-1-INPUT -m tcp -p tcp --dport 22 -j ACCEPT
Save and close the file. Restart iptables:
# service iptables restart

CentOS 7.x/8.x and above commands

Enable and start the sshd service:
# systemctl enable sshd.service
# systemctl start sshd.service

Verify that TCP port number 22 is in listing state using the ss command/netstat command along with the grep command:
ss -tulpn | grep ':22'
ss -tulpn | grep ':22'
Open tcp port 22 using the firewall-cmd command
# firewall-cmd --zone=public --add-service=ssh --permanent
# firewall-cmd --reload

OpenSSH Server Configuration

Edit /etc/ssh/sshd_config, enter:
# vi /etc/ssh/sshd_config
To disable root logins, edit or add as follows:
PermitRootLogin no
Restrict login to user tom and jerry only over ssh:
AllowUsers tom jerry
Change ssh port i.e. run it on a non-standard port like 1235
Port 1235
Save and close the file. Restart sshd:
# service sshd restart ## centos 6.x ##
# systemctl restart sshd.service ## centos 7.x/8.x ##

How to test ssh installation

Use the ssh command/scp command or sftp command as follows:
ssh user@your-server-ip
ssh vivek@server1.cyberciti.biz
ssh vivek@server1.cyberciti.biz uptime
sftp server1.cyberciti.biz
scp foo.gif vivek@ln.cbz01:/home/httpd/images


You learned how to install openssh server (sshd) and clients on CentOS Linux using the yum command. For more information please see the following tutorial:


Posted by: Vivek Gite

The author is the creator of nixCraft and a seasoned sysadmin, DevOps engineer, and a trainer for the Linux operating system/Unix shell scripting. Get the latest tutorials on SysAdmin, Linux/Unix and open source topics via RSS/XML feed or weekly email newsletter.

Start the discussion at www.nixcraft.com

Historical Comment Archive

16 comment




  2. There are a couple/few things I don’t get…
    e.g. for

    Make sure port 22 is opened:
    # netstat -tulpn | grep :22

    What are we *supposed* to see if port 22 *is* opened?

    And for

    Add the line
    -A RH-Firewall-1-INPUT -m state –state NEW -m tcp -p tcp –dport 22 -j ACCEPT

    add it *where*???
    In the :INPUT ACCEPT section?
    in the :OUTPUT ACCEPT section?
    after :COMMIT?

    No matter which line I put it on, when I restart the iptables service I get a red [FAILED] message for that line#.

    And then you change the SSH port to 1235 but don’t revisit iptables?

    What am I missing here?


  3. Thanks a lot!

    Only change :

    -A RH-Firewall-1-INPUT -s -m state –state NEW -p tcp –dport 22 -j ACCEPT


    -A INPUT -s -m state –state NEW -p tcp –dport 22 -j ACCEPT

  4. So,
    Make sure port 22 is opened:
    # netstat -tulpn | grep :22

    What are we *supposed* to see if port 22 *is* open?


    1. If sshd is running. you would expect to see something like:

      # netstat -plunt | grep :22
      tcp 0 0* LISTEN 70813/sshd
      tcp 0 0 :::22 :::* LISTEN 70813/sshd

      If you do not get any output where the IP/port part ends in :22, then you have nothing listening on port 22 (the standard ssh port).


  5. Hi,
    Some thing is wrong.
    Please help resolve it.
    The line 13 is this:
    -A RH-Firewall-1-INPUT -m state –state NEW -m tcp -p tcp –dport 22 -j ACCEPT

    Now when is restart iptables i get this error.

    # service iptables restart
    iptables: Flushing firewall rules: [ OK ]
    iptables: Setting chains to policy ACCEPT: filter [ OK ]
    iptables: Unloading modules: [ OK ]
    iptables: Applying firewall rules: iptables-restore: line 13 failed [FAILED]

  6. You missed something important: If you alter SSH Port, your iptables line –dport needs to be the same as the port you specified, not 22!

    So, if you set: Port 234, then your IP tables entry would be this:
    -A INPUT -m state –state NEW -m tcp -p tcp –dport 234 -j ACCEPT

    To verify your PROPER port is open, the command also needs to reflect the port you altered: netstat -tulpn | grep :234

    Your results should look like this:
    tcp 0 0* LISTEN 26873/sshd
    tcp 0 0 :::234 :::* LISTEN 26873/sshd

    The author should not have suggested changing the port without explaining that the commands and IPTables entries would necessitate being altered as well.

    1. I should have read this comment about 30 minutes ago… lol I was however, able to figure it out on my own. I guess that’s a good thing. :o)

  7. Any changes to iptables *** must *** be on lines above COMMIT, which is found at the end of the file.
    Before adding the port (eg 22), do a search to see if it already exists:
    nano iptables
    Ctrl W to invoke search
    type: dport 22

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